Bond Enthalpy: enthalpy change in breaking bond in molecule of gaseous substance

+ ∆ H = E needed to break bonds

- ∆ H = E released as bond forms

↑ strength bond = ↑  bond enthalpy

↑ strength bond = ↑  stability of cmpd

depends on molecule (variation is sm) so avg values used

∆ H_rxn = ∑ bonds broken - ∑ bonds formed

Example: #57 HW

Bond length: dist bet. nuclei of atoms in bond

↑ # bond bet atoms = ↑  bond enthalpy

↑ # bond bet atoms = ↓ bond length